So...descendent selectors are located in the CSS and what you have here is the HTML. You will start by removing the classes and then structuring the CSS so you have compound selectors that deal with the navigation. The structure for your navigation is a nav tag that has a list in it. Your list is missing tags to make it a list so you will need to fix the list so it has list items (<li>) in it instead of list after list. Once you have the structure correct, you will structure the CSS so you are styling the nav ul li to do what you want it to do.



<style>    
@media (min-width: 321px) and (max-width: 480px) {
nav li {
    column-width: 25%
    text-align: center;
    
}
}

@media only screen and (min-width: 481px) {
    nav li {
        column-width: 100% 
        text-align: left;
    }

}
</style>
    
<nav>
<ul>
    <li><a href="#intro">Intro</a></li>
    <li><a href="#mobile">Mobile First</a></li>
    <li><a href="#features">Features</a></li>
    <li><a href="#links">Links</a></li>
</ul>
</nav>


    
 small {
     
        text-align: left;
    }

large {
    text-align: center;
}